Apparatus for generating sonic vibrations in liquids



Oct. 9, 1962 L. w. CAMP 3,

APPARATUS FOR GENERATING SONIC VIBRATIONS IN LIQUIDS Filed Sept. 8, 1958 FIG.

FIG. 2

INVENTOR. L. W. Camp BY ATTORNEY United States Patent ()fifice 3,058,014 Patented Oct. 9, 1962 3,058,014 APPARATUS FOR GENERATING SONIC VIBRA- TIONS 1N LIQUIDS Leon W. Camp, Santa Monica, Calif., assignor to The Bendix Corporation, a corporation of Delaware Filed Sept. 8, 1958, Ser. No. 759,733 5 Claims. (Cl. 310--8.7)

This invention relates broadly -to transducers for generating sonic (including ultrasonic) vibrations in liquids and to the mounting of such transducers. The invention has particular utility in, although it is not limited to, apparatus for generating sonic waves in a liquid contained in a tank for treating articles submerged in the liquid.

'An object of the invention is to provide an eflicient, simple and inexpensive transducer for generating sonic waves in liquids.

Another object is toprovide a simple, inexpensive and effective wall and. transducer assembly for vibrating liquid on one side of the Wall.

Other more specific objects and features of the invention will appear from the following detailed description of certain embodiments of the invention disclosed in the drawing.

In the drawing:

FIG. 1 is an elevation view, with portions shown in section, of a sonic cleaning tank incorporating the invention.

FIG. 2 is an elevation view, with portions shown in section, of an alternative transducer unit that may be used in FIG. '1.

Referring to FIG. 1, there is shown a sonic cleaning apparatus consisting of a tank having a plurality of identical transducers 11 for creating sonic vibrations in a liquid 12 contained in the tank to increase its cleaning action on objects immersed in the liquid.

The tank 10 may be of any desired shape, but is. here shown as rectangular, having side walls 10a and a bottom wall 10b which is located intermediate the upper and lower ends of the side Walls.

The bottom wall 10b is laminated, consisting of a-first central lamination 14 of an elastomer, such as rubber, a second lamination 15 on the lower surface, and a third lamination 16 on the upper surface. The laminations 15 and 16 are of stiffer material than the first lamination 14 and may be of metal or other strong, stiff material. All three laminations are firmly cemented or bonded together. When the lateral dimensions of the bottom wall are small, both of the stiff laminations 15 and 16 may not be necessary to provide the desired stiffness, and one of them may be eliminated.

The bottom Wall 10b is supported from the side walls 10a by a peripheral flange 18 on the inner surfaces of the side walls. This shoulder 18 is preferably of an elas tomer material which may be bonded to the side walls. It is also desirable to have the second lamination 15 of the'bottom wall stop short of the outeredge of the first, elastomer lamination 14 so that the latter rests directly on the shoulder 18 and is bonded thereto to provide a fluidtight construction. A drain orifice 20 may be provided in the bottom Wall connected at its lower end to a drain hose 22 which may extend through an aperture 23 provided therefor in one of the side walls 10a. Normally the orifice fitting 20 may be closed by a stopper 24.

As shown in FIG. 1, each transducer 11 comprises a longitudinally vibratile element having a hollow cylindrical section 25 of electromechanically-responsive material, a substantially rigid head section 26 on one end thereof, a face plate 27 on the outer face of the head section 26, and a hollow cylindrical mass section 28 on the lower end of the section 25. The sections 25, 26, 27

and 28 are all firmly bonded together to vibrate as an integral unit.

The section 25 may be of any One of many types of electromechanically-responsive material, but is here shown as a ceramic element containing some piezoelectric material, such as barium titanate, which responds to electrostatic forces to change its dimensions. In this instance, the section 25 is energized by applying potential between band electrodes 29 and 30 provided on the outer surface of the element 25. The bands 29 alternate with the bands 30 so that electrostatic fields are produced having a longitudinal component within the section 25, thereby energizing it in longitudinal direction, which is the direction of vibration. It is to be understood that other known methods of electroding may be employed, such as a single electrode covering the inner surface, and another single electrode covering the outer surface.

The head section 26 may be constructed of various materials, such as aluminum. It is purposely relatively thick so as to have rigidity and vibrate as a unit without flexing.

The face plate 27 is relatively thin and is preferably of some hard, corrosion-resistant material, such as stainless steel, to withstand the eroding effects of cavitation.

The mass section 28 on the lower end of section 25 is not essential in all instances, but improves the efficiency of the transducer.

As shown in FIG. 1, the head section 26 is of the same thickness as the first lamination 14 of the bottom wall and fits within an aperture 14a in the lamination, the face plate 27 being of larger diameter than the head section 26 and extending over the margins of the aperture 14a to support the transducer with respect to the lamination 14. The aperture 14a is preferably dimensioned to provide a press fit with respect to the head section 26. The head section 26 and the face plate 27 are preferably bonded to the lamination 14 with a suitable cement to prevent leakage.

The upper, or third, lamination 16 of the bottom Wall 1012 has apertures 16a therein aligned with the apertures 14a, but of larger diameter so that the outer edges of the face plates 27 do not contact the lamination 16. The second lamination 1'5 has apertures 15a therein aligned with the apertures 14a and of larger diameter than the latter, so that the head section 26 does not contact the second lamination. Although the head section 26 is shown in FIG. 1 as having the same thickness as the first lamination 14, this is not necessary, and the head may be of greater thickness than the lamination and extend down through and beyond'the aperture 14a.

The construction of the bottom wall 10b described provides, with the face plate 27 and head sections 26 of the transducers, a rigid, water-tight wall assembly while eliminating any contact between the rigid portions 26v and 27 of the transducers and the rigid portions 15 and 16 of the bottom wall. This provides more eflicientioperation than would be obtainedifthe bottom wall 10b were a simple, rigid wall. The support of the bottom wall 10b from the side Walls 10a by the elastomer shoulder 18 also prevents direct transfer of vibration from the transducer elements to the side Walls 10a, and further increases the efiiciency.

If the liquid 12 is hot, the active material of the transducer may be raised to a temperature above which it is inoperative. Thus, ceramic materials containing barium titanate as the active element become inoperative above a temperature of C. Other piezoelectric ceramic materials are known that are operative over a higher temperature range, but in general they are more expensive than the materials that are limited to a lower operating range.

FIG. 2 shows a transducer construction that may be used in the apparatus of FIG. 1, and may be operated at higher liquid temperatures. In FIG. 2, the separate head section 26 of FIG. 1 is eliminated, and the integral ceramic element a has a lower active section 33, a head section 34, and a motiontransforming section 35. The face plate 27 is bonded directly to the end of the head section 34.

The active section 33 is divided by four slots 37 into four segments of a cylinder, and each segment is provided with alternate sets of electrodes 38 and 39, respectively, which are connected as in FIG. 1. Each electrode 38 or 39 is connected to the corresponding electrode on the next adjacent segment by connectors 40. Each electrode may extend completely around its segment on both the inside and outside surfaces thereof, although this is not essential. The separation of the section 33 into separate segments improves the vibrational characteristics by decreasing the susceptibility to undesired lateral vibrations.

The motion-transforming section is cylindrical on the outside, but of increasing wall thickness from its lower end to the upper end, where it merges with the head section 34.

The chief advantage of the structure shown in FIG. 2 over that shown in FIG. 1 is that the electrically inactive section 35 constitutes a thermal barrier between the head section 34 and the active section 33. This enables the use of liquids of temperature above the temperature at which the ceramic material loses its electromechanical properties, because a substantial temperature gradient will eXist in the motion-transforming section 35.

In general, transducers supported only at the working end, as shown in FIGS. 1 and 2, should be a half wavelength or a multiple of a half wavelength in longitudinal dimension. Usually, in the case of the transducer type shown in FIG. 1, the over-all length is desirably made one-half wavelength. The type of transducer shown in FIG. 2 may be one-half wavelength in over-all length, and preferably the electrically active portion 33 should contsitute one-half or more of the total length.

As a typical example, the transducer of the type shown in FIG. 1 may have the following dimensions for an operating frequency of 20,000 cycles per second:

Inches Diameter of element 25 1.6 Diameter of element 26 2.0 Diameter of element 27 2.5 Thickness of element 25 .25 Thickness of element 26 .25

Thickness of element 27 .040

Internal diameter of element 28 1.1 Length of element 28 .5 Radial thickness of element 28 .25

The dimensions of a transducer of the type shown in FIG. 2 for operation at 20,000 cycles per second may be as follows:

Inches Outside diameter of sections 35, 34 and 33 1.6 Thickness of section 33 .25

4 Length of section 34 .25 Length of section 35 1.0 Length of section 33 2.0

Although for the purpose of explaining the invention a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. Apparatus for generating sonic vibrations in liquids comprising:

a vibratile element including a substantially rigid head having an outer face for imparting vibrations to a liquid in contact therewith, and means for vibrating said head in direction normal to said outer face;

a face plate on said outer face of said head substantially thinner than the head and having edge portions projecting beyond the peripheral edge of the head and means securing the face plate to said outer face of the head for vibration therewith;

means constituting a liquid barrier between said vibrating means and the front face of said face plate including a wall having an aperture in which said head is positioned with said face plate and said vibrating means on opposite sides of said wall, respectively, said projecting edge portions of said face plate overlapping and engaging the marginal portion of said wall defining said aperture;

said wall comprising a first lamination of elastomeric material of substantial thickness juxtaposed to said head and a second lamination of stiffer material on one face of said first lamination.

2. Apparatus according to claim 1 including additional walls defining with said mentioned wall a liquid-retaining tank, only said first lamination of said wall being joined to said additional Walls.

3. Apparatus according to claim 1 in which that portion of said aperture in said first lamination is a press fit with said head and that portion of said aperture in said second lamination is larger than said head.

4. Apparatus according to claim 3 in which said wall includes a third lamination of stiffer material than said elastomer material on the other face of said first lamination.

5. Apparatus according to claim 3 in which said second lamination is on that face of said first lamination overlapped by said face plate and the aperture in said second lamination is larger than said face plate whereby said edge port-ions of said face plate contact said first lamination and do not contact said second lamination.

References Cited in the file of this patent UNITED STATES PATENTS 2,406,792 Beniolf Sept. 3, 1946 2,616,223 Jonker Nov. 4, 1952 2,638,557 Harris May 12, 1953 2,803,803 Jonker et al Aug. 20, 1957 2,815,193 Brown Dec. 3, 1957 2,848,672 Harris Aug. 19, 1958 2,874,316 Murdock Feb. 17, 1959 

